American Oil and Gas Reporter - November 2019 - 54

SpecialReport: Marcellus/Utica Activity
The LE technique restricts the number
of perforations while utilizing a sufficient
injection rate to restrict perforation capacity, thereby diverting treatment to a
greater portion of the perforated interval.
Although developed for conventional
wells to compensate for variations in bottom-hole fracture pressure, the concept
applies equally to an unconventional stage
where heel clusters preferentially take
treatment to the detriment of toe clusters.
VSC builds on the concept of LE by restricting fluid flow even further, utilizing
fewer perforations in zones that preferentially take treatment (heel clusters) and
more perforations in the understimulated
toe clusters.
The downhole camera was used to inspect perforations for visible signs of
erosion associated with slurry exiting the
perforation. A semiquantitative ranking
scheme was established to characterize
the amount of erosion and place each
perforation in one of three categories:
major erosion, minor erosion or no erosion.
Five perforating schemes were tested-
four geometric shot clusters (GSC)
schemes (where an equal number of perforations was used in each cluster) and

one VSC scheme-with variations in the
number of clusters, cluster spacing, perforations per cluster and perforations per
stage (Table 1). All stages used 0.43inch entry-hole diameter perforations,
200-foot stage lengths, and 15% 100mesh and 85% 40/70-mesh proppant.
24-Stage Well Results
Figure 2 shows the results of all 24
stages in one Marcellus well. Consistent
heel-ward bias is seen in nearly all stages,
independent of the perforating scheme,
number of clusters or cluster spacing. It
also is evident that the toe cluster(s) were
not treated effectively, as evidenced by
the absence (or limited amount) of perforation erosion in the toe cluster(s).
In order to create a quantitative metric
to compare the impact of the perforating
scheme used in each stage, the following
assumptions were made regarding proppant volumes exiting each category of
perforation: Major erosion perforations
accepted both 100- and 40/70-mesh sand,
minor erosion perforations accepted only
100-mesh, and no erosion perforations
accepted no sand. Applying these assumptions consistently made it possible

TABLE 1
Perforating Schemes Tested
Design
1
2
3
4
5

Perf Scheme
6-6-6-6-6-6-6-6
6-6-8-10-10
8-8-8-8-8
6-6-6-6-6-6
10-10-10-10

Clusters
8
5
5
6
4

Cluster Spacing (ft) Shots/Cluster
23
6
40
6-10 (VSC)
40
8
32
6
53
10

Total Perfs
48
40
40
36
40

FIGURE 2
Semiquantitative Ranking of Perforation Erosion
(Heel Stages at Top; Toe Stages at Bottom)
Major

18

17

16 15

14

None

13

Not Observed

12 11

Toe

Heel

24 23 22 21 20 19

Minor

54 THE AMERICAN OIL & GAS REPORTER

10

90% Sand Length

9

8

7

6

5

4

3

2

1B

1

to develop a representative metric for
comparing the stimulated portion of each
stage: the 90% sand length.
The 90% sand length was calculated
by summing the cumulative volume of
sand each perforation accepted (total respective proppant volume divided by
number of perforations accepting each
respective mesh size) until 90% of the
total volume of proppant pumped in each
stage was reached. Then the distance of
the coinciding perforation from the heelmost perforation was determined based
on the perforating scheme, resulting in a
length figure. Based on this metric, the
perforating scheme utilized had no impact.
Even though the stage lengths were all
200 feet (plug to plug), the top and bottom
perforations both were offset 20 feet from
the respective plugs, so the maximum
achievable length was 160 feet.
Geochemical water tracers also were
employed. In general, no correlation was
seen between the stimulated interval of
each stage as defined via the 90% sand
length and the relative volume of tracer
recovered, with one notable exception:
stage 10, one of the few exceptions to
the persistent heel-ward bias seen throughout all stages and perforating schemes.
In addition, the 90% sand length for
stage 11 was the lowest recorded in any
of the 24 stages. The heel of stage 10 and
the toe of stage 11 seem to represent a
contiguous understimulated interval in
the well, and the relative tracer contributions returned from these stages is small
when compared with stages 9 and 12
above and below. We have no explanation
for this, other than the tracer results seem
to corroborate that something out of the
ordinary occurred in stages 10 and 11.
Controlling Factor
In order to determine the influence of
geomechanical properties on perforation
erosion, the stratigraphic position of each
perforation was output from the geosteering interpretation of the lateral. The
results show that for a given stratigraphic
position, all possible categories of perforation erosion occur. Since geomechanical properties are primarily a function
of stratigraphic position, the geomechanical properties associated with the position
of a given perforation appear to have no
impact on the amount of proppant that
perforation accepts.
However, one factor controlling proppant distribution that stands out is EFA,
or the combined area of all perforations.
American Oil and Gas Reporter - November 2019

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